Lever-retarding accessory for dental engine



J.M.CLAUSER ETAL LEVER-RETARDING ACCESSORY FOR DENTAL ENGINE Filed May10. 1954 '/Z5 I 5 1 2/ 7L J; l

INVENTORQ United States PatentO LEVER-RETARDING ACCESSORY FOR DENTAL 2ENGINE John M. Clauser and Frederick K. Clauser, St. Louis, Mo.,assignors to Midvale Dental Supply Company, St. Louis, M0., acorporation ofMissouri Application May 10, 1954, Serial No. 428,458 g 6Claims. 01. 201-48 This invention relates in general to controllers fordental engines and, more particularly, to a lever-retarding accessorytherefor. The invention is particularly adapted for engines operatedatthe relatively high speeds of 12,000 R. P. M. which is a recentdevelopment in dental practice.

Dental engines for operating discs and burrs are usually driven byelectric motors which have associated therewith a speed controllernormally located on the floor and including a horizontally movable leverhaving a pedal portion at each of its ends for operation by the usersfoot. Connected to the lever is a control arm for progressive movementacross a series or shunt resistance, fixed contacts arrangedconcentrically of the controller for increasing or decreasing the enginespeed. Contacts on one side of the median line of the controller causerotation of themotor in one direction-while the contacts on the otherside of said line will effect rotation in the opposite or reversedirection. The lever is biased into off position by return springs, sothat upon release of the lever from any one of its circuit-closingpositions, the same will be automatically swung to move the control armto circuit-open position.

On release of the lever from high speed position, wherein the shuntresistance is open, it will rapidly accelerate under influence of thesprings with the interval of travel from such position to off positionbeing relatively short. Ithas been noted that during such interval, awell-developed sparking takes place between the commutator and brushes.Such sparking is intense enough to cause pitting of the commutator and aburning of the brusheswhich materially decrease engine effectiveness,requiring periodic replacement of parts. If the movement of the leverfrom high speed to off position be retarded sufficiently, sparkingbetween the commutator and brushes is reduced to non-damagingproportions.

Assumedly, the destructive sparking is due to selfinductive flow ofcurrent which occurs across the brushes; also,'the short-circuitingaction of the brushes on the coils brought out to the commutatorsegments; also, the electro-motive force generated by the armature underits own momentum after the circuit is opened.

It the control lever moves slowly enough towards off position, theeffects noted above are decreased to an extent that the destructivesparking is avoided.

The main object of the present invention is to slow the return of thecontrol lever upon the operators release of the pedal and avoid therapid action otherwise resulting from the force of the return springs.

Another object is to provide an accessory for ready application to acommon form of pedal and lever of a dental engine controller for slowingdown the action of the lever-return-spring and activated by the speed ofthe lever.

Another object is to utilize the inertia of a weight applied to thecontrol lever to obtain the slowing down effect.

Another object is to provide an accessory for application to acontroller leverand pedal which will provide frictional resistance tothe action of the lever-returnspring in order that the lever may movemore slowly from high speed to off position.

Another object is to provide an accessory of the character stated whichcan be cheaply manufactured; which may be installed upon the lever byunskilled individuals;

which may be adapted for use with various types of lever mounting and anassociated foot-actuated controller to which the invention may beapplied. 1

Figure 2 is a fragmentary side view of the controller provided with alever retarding accessory embodying the present invention.

Figure 3 is a fragmentary top plan view of the accessory shown in Figure2; and related controller mechanism.

Figure 4 is a perspective view of another form of leverretardingaccessory constructed in accordance with the present invention.

Figure 5 is a fragmentary side view of a controller lever and pedalprovided with an accessory of the form shown in Figure 4.

The dental engine 1 is mounted on a supporting yoke conventional typefoot controller having a cylindrical casing 5 with a'rcuate openings 6in the sides thereof through which extends a. horizontally movable lever7 pivoted at P and enlarged at its ends to form pedals 8. Movement ofthe lever by either pedal in clockwise or anti-clockwise directionshifts a well-known rheostat device to start and accelerate the motorstep by step according to the positions determined by the operator. Suchmovement elongates one of springs S and when the pedal is moved toreturn the lever to normal off position, the spring ordinarily wouldaccelerate the lever movement to such extent as to result in undesirablesparking.

To avoid this result, there is mounted upon each pedal 8 alever-retarding accessory comprising a pair of parallel side plates 9,10 atopposite sides of pedal 8 and spaced apart by rivets 11 and sleeves12 above and below the pedal. Plate 9 has an extension 13 projectingacross and above lever 7 with its lower edge resting on the upper faceof the lever, spaced from the inner end of pedal 8. Extension 13terminates in a flange 14 turned inwardly toward controller casing 5,parallel to plates 9, 10. Mounted upon flange 14 by pivot pin 15 is anormally vertically disposed rocker arm 16 projecting in its lowerportion downwardly beyond lever 7 and having its lower end weighted, asat 17. The upper portion of rocker arm 16 forms a clevis 18 openingtoward controller casing 5 for supporting a rotatable pin 19 whichmounts a friction wheel 20 of rubber or similar material. Friction wheel20 will normally be in immediate proximity, but out of contact with,controller casing 5.

When the operator releases foot pressure on pedal 8 and lever 7 and aspring S rotates the lever from high speed position to off position, thelower weighted end of rocker arm 16 will swing outwardly throughcentrifugal force as the lever is accelerated, causing wheel 20 tofrictionally engage controller casing 5, as indicated in dotted lines inFigure 2. The braking action so produced partially counteracts the forceof the return spring, whereon Patented Apr. 29, 1958 body, having aweight of about one pound, and prefen,

ably having parallel side walls 21, 22, and arcuate ,top wall 23, andbeing-cut away in its lower portion at its normally inner end to providea shoulder24. Walls 21, 22 are spaced apart a distance substantiallyequal to the thickness of pedal 8 and may 'bepress'ed :towards eachother to be secured to the lever. Shoulder. 24 will overlie lever 7,which is of greater width than the thickness of lever 8, as shown at 7'in Figure "3.

Upon release of lever .7 .from .footpressure, the inertia or weight willresist the force of the lever-return springs so that lever 7 will beslowly returned to off position, as the spring overcomes 'thei'inertiaof the weighted pedal. With this type of retarding or snubbing device,the control arm on lever 7 will move more slowly as the lever returns tooff position, whereby sparking is effectively reduced or eliminatedbetween the commutator and brushes. vAn additional advantage is that-thedeceleration of the motor avoids the likelihood of the motor beltjumpingfrom its pulleys to the annoyance and interruption of theoperator.

The lever-retarding accessory of the present invention can be readilyapplied to the pedal ofany type of controller, irrespective of design ofsuch pedal. No modification or alteration of the pedal is required toproperly apply the accessory thereto and it is apparent that the samemay be mounted without the exercise of skill on the part of the user.The accessory is so constructed as to be securely engaged upon the leverpedal so that inadvertent displacement is avoided.

The details of construction may be varied otherwise than as indicatedwithout departing from the spirit of the invention and the exclusive useof those modifications coming within the scope of the claims iscontemplated.

What is claimed is:

1. In combination with a dental engine motor controller, including ahousing having a side wall provided with an elongated slot, there beinga rheostat lever projecting through said slot and terminating in a pedalfor engagement by an operator and provided with a spring for moving thelever to a normal off position, a weight device readily applicable tosaid pedal and movable therewith and operated automatically upon releaseof the operators thrust on said pedal to retard, by its inertia, thespeed of the return movement of said'lever and controller throughout theextent of the return movement.

2. For use with a dental engine controller having a spring-biasedoperating lever with a pedal formed at its end, an accessory for saidpedal to resist the force of the lever spring comprising a body forapplication upon the pedal, and a friction element rockably carried onsaid body for movement towardsaid controller through centrifugal forceon spring-actuated swinging of said lever to engage said controller forretarding swinging of said lever.

3. For use with a dental engine controller having a spring-biasedoperating, lever with a pedal formed at its end, an accessory for saidpedal to resist the force of the a lever spring comprising a body forapplication .upon the pedal, and an arm rockably carried on said body atthe inner end thereof, said arm being of increased weight at its lowerend, and a friction element carried at the upper end of said arm forengagement withthe controller on rocking of the arm through centrifugalforce.

4. For 'use'with aderrtal engine controller having aspring-biasedoperating lever with a pedal formed at its end, anaccessory for said pedal to, resist the force of thelever springcomprising a body for application upon the pedal, and an arm rockablycarried on said body at the inner end thereof, said arm being Weighted apredetermined amount at its lower 'end, a yieldable friction elementcarried at the upper end of said 'arm in confronting relation tosaid'controller for engagement therewith on rocking of the arm throughcentrifugal force.

' 5. In combination with a dental engine having a motor anda rheostattype control including a horizontally disposed radial levcr pivoted nearone end and movable under thrust-by an operator, applied to its otherend, from an off position to successively higher-speed operativepositions, there being a spring returning said lever to off positionwhen released trom'said thrust, a weight detachably mounted on saidlever near its outer end and forming an inertia device resistingacceleration in the return movement ofthe released lever 10 0E positionby said spring.

6. In combination with a dental engine motor controller, including ahousing having a side wall provided with an elongated slot, there beinga'rheostat lever projecting through said slot'and terminating in ahorizontally movable pedal for lateral thrust by an operator andprovided with a spring for 'returningthe lever to a normal or? position,a separately formedweight device readily applicable to-said pedal andmovable'therewithand acting automatically, by'its inertia,'upon releaseof'the operators thrust on said pedal to retard the spring-inducedreturn movement of said lever until the lever reaches its normal offposition.

References Cited in the file of this patent v UNITED' STATES PATENTS

